MODULATION OF LEAF ELONGATION, TILLER APPEARANCE AND TILLER SENESCENCE IN SPRING BARLEY BY FAR-RED LIGHT

Supplemental far-red (FR) illumination of light-grown grass seedlings inhibits tiller production while enhancing leaf elongation. Although m uch is known about FR enhancement of internode elongation in dicots, r elatively little research has been conducted to determine the effects of FR on monocot development. In growth chamber experiments, fibre opt ics were used to direct supplemental FR to elongating leaf blades, mai n stem bases and mature leaf blades of light-grown barley (Hordeum vul gare L.) seedlings. Our objective was to identify specific sites of pe rception for FR enhancement of leaf elongation and inhibition of tille r production, and to assess potential FR effects on tiller senescence. Far-red illumination of elongating leaves or of the main stem base re duced the total number of tillers per plant, primarily by reducing sec ondary and tertiary tiller production, and enhanced leaf elongation. H owever, leaf elongation was less sensitive to stem base treatments tha n to illumination of the elongating blade. Increased leaf length resul ted from increased leaf elongation rate, while the duration of leaf el ongation was unaffected. Exposure of mature leaf blades to FR had no e ffect on tillering or leaf elongation. None of the FR treatments led t o tiller senescence. Localization or FR perception in vertically orien ted tissues such as elongating blades and stem bases permits early det ection of reflected light from neighbouring plants, allowing rapid res ponse to impending competition.